1. Field Of the Invention
The present invention relates to computer systems. More particularly, the present invention relates to a system and method for remote distributed program verification using API definitions.
2. Background
In general, computer programs are written as source code statements in a high level language that is easy for a human being to understand. As the computer programs are actually executed, a computer responds to machine code, which consists of instructions comprised of binary signals that directly control the operation of a central processing unit (CPU). A special program called a compiler is typically used to read the source code and to convert its statements into the machine code instructions of the specific CPU. The machine code instructions thus produced are platform dependent, that is, different computer devices have different CPUs with different instruction sets indicated by different machine codes.
More powerful programs are typically constructed by combining several simpler programs. This combination can be made by copying segments of source code together before compiling and then compiling the combined source. When a segment of source code statements is frequently used without changes, it is often preferable to compile it once, by itself, to produce a module, and to combine the module with other modules only when that functionality is actually needed. This combining of modules after compilation is called linking. When the decision on which modules to combine depends upon run time conditions and the combination of the modules happens at run time, just before execution, the linking is called dynamic linking.
Object Oriented Principles
Object oriented programming techniques such as those used by the Java™ platform are widely used. The basic unit of object oriented programs is an “object”. An object has methods (procedures) and fields (data). The term “members” is used herein to refer to methods and fields. A method declares executable code that can be invoked and that passes a fixed number of values as arguments. A class defines the shared members of the objects. Each object then is a particular instance of the class to which it belongs. In practice, a class is a template to create multiple objects (multiple instances) with similar features.
One property of classes is encapsulation. Encapsulation is used to describe a system wherein access to an object is provided through an interface, while keeping the details private. In other words, the actual implementation of the members within the class is hidden from an outside user and from other classes, except as exposed by an interface. This makes classes suitable for distributed development, for example by different developers at different sites on a network. A complete program can be formed by assembling the classes that are needed, linking them together, and executing the resulting program.
Classes enjoy the property of inheritance. Inheritance is a mechanism that enables one class to inherit all of the members of another class. The class that inherits from another class is called a subclass; the class that provides the attributes is the superclass. Symbolically, this can be written as subclass<=superclass, or superclass=>subclass. The subclass can extend the capabilities of the superclass by adding additional members. The subclass can override a virtual method of the superclass by providing a substitute method with the same name and type.
The members of a class type are fields and methods; these include members inherited from the superclass. The class file also names the superclass. A member can be public, which means that it can be accessed by members of the class that contains its declaration. A member can also be private. A private field of a class is visible only in methods defined within that class. Similarly, a private method may only be invoked by methods within the class. Private members are not visible within subclasses, and are not inherited by subclasses as other members are. A member can also be protected.
An interface type is a type whose members are constants and abstract methods. This type has no implementation, but otherwise unrelated classes can implement it by providing implementations for its abstract methods. Interfaces may have sub-interfaces, just as classes may have subclasses. A sub-interface inherits from its super-interface, and may define new methods and constants as well. Additionally, an interface can extend more than one interface at a time. An interface that extends more than one interface inherits all the abstract methods and constants from each of those interfaces, and may define its own additional methods and constants.
Java™ Programming Language
In the Java™ programming language, classes can be grouped and the group can be named; the named group of classes is a package. If a class member is not declared with any of the public, private or protected keywords, then it is visible only within the class that defines it and within classes that are part of the same package. A protected member may be accessed by members of declaring class or from anywhere in the package in which it is declared. The Java™ programming language is described in detail in Gosling, et al., “The Java™ Language Specification”, August 1996, Addison-Wesley Longman, Inc.
Java™ Virtual Machine
Programs written in the Java™ language execute on a Java™ virtual machine (JVM), which is an abstract computer architecture that can be implemented in hardware or software. Either implementation is intended to be included in the following description of a VM. For the purposes of this disclosure, the term “processor” may be used to refer to a physical computer or a virtual machine.
A virtual machine is an abstract computing machine generated by a software application or sequence of instructions that is executed by a processor. The term “architecture-neutral” refers to programs, such as those written in the Java™ programming language, which can be executed by a virtual machine on a variety of computer platforms having a variety of different computer architectures. Thus, for example, a virtual machine implemented on a Windows™-based personal computer system will execute an application using the same set of instructions as a virtual machine implemented on a UNIX™-based computer system. The result of the platform-independent coding of a virtual machine's sequence of instructions is a stream of one or more bytecodes, each of which is, for example, a one-byte-long numerical code.
The Java™ Virtual Machine (JVM) is one example of a virtual machine. Compiled code to be executed by the Java™ Virtual Machine is represented using a hardware- and operating system-independent binary format, typically stored in a file, known as the class file format. The class file is designed to handle object oriented structures that can represent programs written in the Java™ programming language, but may also support several other programming languages. These other languages may include, by way of example, Smalltalk. The class file format precisely defines the representation of a class or interface, including details such as byte ordering that might be taken for granted in a platform-specific object file format. For the sake of security, the Java™ Virtual Machine imposes strong format and structural constraints on the instructions in a class file. In particular example, JVM instructions are type specific, intended to operate on operands that are of a given type as explained below. Any language with functionality that can be expressed in terms of a valid class file can be hosted by the Java™ Virtual Machine. The class file is designed to handle object oriented structures that can represent programs written in the Java™ programming language, but may also support several other programming languages. The Java™ Virtual Machine is described in detail in Lindholm, et al., “The Java™ Virtual Machine Specification”, April 1999, Addison-Wesley Longman, Inc., Second Edition.
The process of programming using such a VM then has two time periods associated with it; “compile time” refers to the steps which convert the high level language into VM instructions, and “run time” refers to the steps which, in a Java™ VM environment, interpret instructions to execute the module. Between compile time and run time, the modules of instructions compiled from statements can reside dormant for extended, arbitrary periods of time, or can be transferred from one storage device to another, including being transferred across a network.
Loading refers to the process of finding the binary form of a class or module with a particular name, typically by retrieving a binary representation previously compiled from source code. In the JVM, the loading step retrieves the class file representing the desired class. The loading process is implemented by the bootstrap loader or a user defined class loader. A user-defined class loader is itself defined by a class. A class loader may indicate a particular sequence of locations to search in order to find the class file representing a named class.
Linking in the JVM is the process of taking a binary form of a class in memory and combining it into the run time state of a VM, so that it can be executed. A class is loaded before it is linked.
Verification
For many reasons, particularly regarding the integrity of downloaded computer programs, the Internet and other insecure communication mediums are potentially “hostile” environments. A downloaded program may contain errors involving the data types of operands not matching the data type restrictions of the instructions using those operands, which may cause the program to fail during execution. Even worse, a program might attempt to create object references (e.g. by loading a computed number into the operand stack and then attempting to use the computed number as an object handle) and to thereby breach the security and/or integrity of the user's computer. Alternatively, one or more of the modules may have been updated since the others were prepared. It is therefore prudent, when assembling several modules that may have been written independently, to check both that (1) each module properly adheres to the language semantics and that (2) the set of modules properly adheres to the language semantics. These checks are typically performed on program modules containing instructions produced from compiled source code. By analogy with the terminology used by the designers of the Java™ programming language, this post-compilation module checking can be called verification. A verifier, therefore, performs an essential role in ensuring a secure runtime environment.
The binary classes of the JVM are examples of general program modules that contain instructions produced from compiled source statements. Context sensitivity of validity checks performed during verification means that those checks depend on information spread across more than one module, i.e., those checks are called inter-module checks herein. Validity checks that do not require information from another module are called intra-module checks herein. Intra-module checks include, for example, determining whether the downloaded program will underflow or overflow its stack, whether any instruction will process data of the wrong type and whether the downloaded program will violate files and other resources on the user's computer. See, for example, U.S. Pat. No. 5,668,999 to Gosling, U.S. Pat. No. 5,748,964 to Gosling and U.S. Pat. No. 5,740,441 to Yellin et al.
During normal execution of programs using languages that do not feature preexecution verification, the operand stack must be continuously monitored for overflows (i.e., adding more data to the stack than the stack can store) and underflows (i.e., attempting to pop data off the stack when the stack is empty). Such stack monitoring must normally be performed for all instructions that change the stack's status (which includes most all instructions). For many programs, stack monitoring instructions executed by the interpreter account for approximately 80% of the execution time of an interpreted computer program.
Turning now to FIG. 1, a high level flow diagram that illustrates verification is presented. At 10, intra-module checks are performed to determine whether a module is internally consistent. At 20, inter-module checks are performed to determine whether the module is consistent within the context of externally referenced modules. Verification is successful if both checks pass. Execution of a module is prevented if either checks fail.
Verification typically follows an execution path. Verification starts at a program's main entry point and proceeds in a “top down” fashion, one instruction at a time. During this process, the verifier may encounter a reference to an external library that includes at least one program unit. At this point, the verifier obtains the binary file for the external library and continues verification along an execution path.
Turning now to FIG. 2, a high level flow diagram that illustrates verification of an application to be executed on a resource-rich device 62 is presented. Verification is typically performed on a relatively resource-rich device 62 such as a desktop computer. A compiler 50 compiles a source file 55. During compilation, the compiler 50 verifies the correct use of data and instructions. These checks include intra-module checks and inter-module checks. The output of the source code compiler 50 is a binary file 60 containing the executable instructions corresponding to the source file 55. When the binary file 60 is referenced by an application executing on a virtual machine 65, a loader 70 loads the binary file 60. A verifier 75 verifies the binary file 60 at some point prior to execution by an interpreter 80. If the binary file 60 references any items that are external to the binary file 60, the verifier 75 verifies the binary file 60 against the referenced binary file(s) 60 containing the externally referenced item(s).
Turning now to FIG. 3, a block diagram that illustrates the need for verification is presented. FIG. 3 is the same as FIG. 2, except that binary file 110 and/or referenced binary file 107 are potentially modified at some point after source file 105 is compiled. The modification may be the result of an update of a binary file 110 or referenced binary file 107. Alternatively, modification of the binary file 110 or referenced binary file 107 may be the result of file corruption. As mentioned previously, such program modifications could potentially cause the program to violate Java™ semantics and thus breach the security and/or integrity of the host computer 155.
Note that some updates in FIG. 3 are allowed. Some changes made when revising a binary file result in the new version being backward compatible with the previous version. When a newer version is backward compatible with an older version, the versions are said to be binary compatible. Binary compatibility is discussed in greater detail below. A verification error should be indicated when versions are not binary compatible. Thus, some updates may pass verification, but corrupted binary files must not pass verification.
Verification coupled with execution time has some disadvantages. For example, in an object oriented programming language system like the Java™ platforms (but not Java Card™ platforms), it leads to a verifier initiating class loading when the verifier needs to check subtype relations among classes not already loaded. Such loading can occur even if the code referencing other classes is never executed. Because of this, loading can consume memory and slow execution at run time as compared to a process that does not load the classes unless they are referenced by the instructions that are actually executed.
Methods for verification coupled with execution time typically do not verify one class or module at a time before run time. This is a disadvantage because classes cannot be verified ahead of time, e.g. before run time, so verification must incur a run time cost. Thus, there is a need for module-by module, also called module-at-a-time, verification before run time. Such verification is also called pre-verification because technically it is distinct from the verification which occurs during run time linking by the Java Card™ Virtual Machine (JCVM).
Also, since verification is typically performed at run time, a class that has been run once, and passed verification, is subjected to verification again each time the class is loaded—even when reverification is not required. Reverification may not be required, for example, when the class is being used in the same application on the same processor, or in an environment that prevents changes that would affect verification. This can lead to redundant verification, thereby requiring more memory and executing more slowly during run time than ought to be necessary. Thus, there is a need for an option to use verified modules without further, or with minimum verification at run time.
Resource-Constrained Devices
Resource-constrained devices are generally considered to be those that are relatively restricted in memory and/or computing power or speed, as compared to typical desktop computers and the like. Other resource-constrained devices include, by way of example, smart cards, cellular telephones, boundary scan devices, field programmable devices, personal digital assistants (PDAs) and pagers and other miniature or small footprint devices.
Smart cards, also known as intelligent portable data-carrying cards, are a type of resource-constrained device. Smart cards are typically made of plastic or metal and have an electronic chip that includes an embedded microprocessor or microcontroller to. execute programs and memory to store programs and data. Such devices, which can be about the size of a credit card, typically have computer chips with 8-bit or 16-bit architectures. Additionally, these devices typically have limited memory capacity. For example, some smart cards have less than one kilobyte (1 K) of random access memory (RAM) as well as limited read only memory (ROM), and/or non-volatile memory such as electrically erasable programmable read only memory (EEPROM).
A Java™ virtual machine executes programs written in the Java™ programming language and is designed for use on desktop computers, which are relatively rich in memory. It would be desirable to write programs that use the full implementation of the Java™ virtual machine for execution on resource-constrained devices such as smart cards. However, due to the limited architecture and memory of resource-constrained devices such as smart cards, the full Java™ virtual machine platform cannot be implemented on such devices. Accordingly, a separate Java Card™ (the smart card that supports the Java™ programming language) technology supports a subset of the Java™ programming language for resource-constrained devices.
Referring to FIG. 4, development of an applet for a resource-constrained device, such as a smart card 160, begins in a manner similar to development of a Java™ program. In other words, a developer writes one or more Java™ classes and compiles the source code with a Java™ compiler to produce one or more class files 165. The applet can be run, tested and debugged, for example, on a workstation using simulation tools to emulate the environment on the card 160. When the applet is ready to be downloaded to the card 160, the class files 165 are converted to a converted applet (CAP) file 175 by a converter 180. The converter 180 can be a Java™ application being executed by a desktop computer. The converter 180 can accept as its input one or more export files 185 in addition to the class files 165 to be converted. An export file 185 contains naming or linking information for the contents of other packages that are imported by the classes being converted.
Referring to FIG. 5, the CAP format is parallel to the class file information. Each CAP 250 contains all of the classes and interfaces defined in one Java™ package. A CAP file 250 has a compact and optimized format, so that a Java™ package can be efficiently stored and executed on resource-constrained devices. Among other things, the CAP file 250 includes a constant pool component (or “constant pool”) 255 that is packaged separately from a methods component 260. The constant pool 255 can include various types of constants including method and field references which are resolved either when the program is linked or downloaded to the smart card or at the time of execution by the smart card. The methods component 260 specifies the application instructions to be downloaded to the smart card and subsequently executed by the smart card. Also included in a CAP file 250, among other things, are class definitions 265, field definitions 275, and descriptive type definitions 275.
Referring again to FIG. 4, after conversion, the CAP file 175 can be stored on a computer-readable medium 170 such as a hard drive, a floppy disk, an optical storage medium, a flash device or some other suitable medium. Or the computer-readable medium can be in the form of a carrier wave, e.g., a network data transmission or a radio frequency (RF) data link.
The CAP file 175 then can be copied or transferred to a terminal 190 such as a desktop computer with a peripheral card acceptance device (CAD) 195. The CAD 195 allows information to be written to and retrieved from the smart card 160. The CAD 195 includes a card port (not shown) into which the smart card 160 can be inserted. Once inserted, contacts from a connector press against the surface connection area on the smart card 160 to provide power and to permit communications with the smart card 160, although, in other implementations, contactless communications can be used. The terminal 190 also includes an installation tool 200 that loads the CAP file 175 for transmission to the card 160.
The smart card 160 has an input/output (I/O) port 205 which can include a set of contacts through which programs, data and other communications are provided. The card 160 also includes a loader 210 for receiving the contents of the CAP file 175 and preparing the applet for execution on the card 160. The installation tool 210 can be implemented, for example, as a Java™ program and can be executed on the card 160. The card 160 also has memory, including volatile memory such as RAM 240. The card 160 also has ROM 230 and non-volatile memory, such as EEPROM 235. The applet prepared by the loader 210 can be stored in the EEPROM 235.
As mentioned regarding FIG. 2, verification is typically performed on a resource-rich device. Verification programs are typically large programs that require a relatively large amount of runtime memory when executing. Also, verifier programs typically require large amounts of detailed descriptive information in the verification process. This descriptive information includes information regarding field types, signature types and access flags (private, protected, etc). This type information is typically maintained in secondary storage. Such memory requirements are typically not an issue on relatively resource rich devices such as a desktop computer. However, these same characteristics make verification ill-suited for resource-constrained devices such as smart cards. Providing verification of program modules to execute on a resource-constrained device is critical to ensure the integrity of program modules executed such a device. Accordingly, a need exists in the prior art for a system and method for remote verification of programs to be executed by a resource-constrained device.
As mentioned previously, a Java™ verifier proceeds along an applet's execution path, verifying all external references in the process. This means that the verifier must have access to the full binary file of not only the module to be verified, but also all modules in the execution path of the module to be verified. However, some of the libraries may contain proprietary implementations that must not be revealed to consumers. For example, a vendor may install a library that contains proprietary implementation algorithms (such as an encryption algorithm) that must not be revealed to another vendor. Since typical verification methods require revealing the binary files of to the modules to be verified, such methods could reveal proprietary information. Accordingly, there is a need in the prior art for a system and method for program verification that does not reveal proprietary details.
Moreover, a library may have multiple implementations. Verification with a particular implementation does not guarantee verification with another implementation. Accordingly, there is a need in the prior art for a system and method for specifying when verification with a first implementation guarantees verification with a second implementation.
Program Module Hierarchical Dependencies
FIG. 6 shows a diagram illustrating typical hierarchical dependencies among a group of program packages (including both libraries and program applets) loaded onto a smart card. Applications may be loaded onto smart card incrementally and linked on-card for execution so that the functionality of the smart card may be updated with additional capabilities in addition to factory-programmed functionalities. In the diagram, a Java™ language framework 285 and a Java Card™ framework 280 exist at a Java Card™ API level. Above the Java Card™ API level is a custom API level with one or more custom frameworks 290. The custom framework 290 may be supplied by one or more value added providers through various software development kits (SDKS) to extend an existing framework or other API. At the highest level is an application level where various applets 295, 300 and 305 reside.
Each of the boxes shown in FIG. 6 represents a Java™ package. A package is called a library package if it exports items and is therefore referenced by other packages. A package is called an applet package if it contains a program entry point. Some packages are both library and applet packages.
As shown in FIG. 6, a package may depend on other packages at the same API level or from those packages in lower API levels. The Java Card™ framework 280 may have dependencies from the Java™ language framework 285. Moreover, the custom framework 290 at the custom API level and the applets 300 and 305 may have references that depend from the Java Card™ framework 280. In turn, the applet 295 may have references that depend on the custom framework 290. The applet 295 and the custom framework 290 may also depend on the Java™ language framework 285. Applets may also depend on one another as shown by the line from Applet 305 to Applet 300. In this case, Applet 300 is both an applet and library package.
Although the example of FIG. 6 shows linear dependencies, non-linear dependencies such as circular dependencies may be supported using a suitable converter and installation tool.
Post-issuance Install
The Java Card™ CAP file format provides for the post issuance installation of applications. In other words, the CAP file allows the content of a resource-constrained device to be updated after the device has been issued to an end user. The capability to is install applications after the card has been issued provides card issuers with the ability to respond dynamically to their customer's changing needs. For example, if a customer decides to enroll in the frequent flyer program associated with the card, the card issuer can add this functionality, without having to issue a new card.
The Java Card™ CAP file format thus provides more flexibility for application issuers. Application issuers may implement transactional services as applets, and then host these applets, either in their own cards or in the cards of other issuers with whom they do business. For example, an issuer may provide a core service to clients in the form of Java™ applets for the issuer's cards. The clients will then combine these applets with other applets designed to provide a variety of value added services. These applet combinations can be updated through the dynamic applet loading process to meet the changing needs of individual customers.
Turning now to FIG. 7, a block diagram that illustrates preparation of a resource-constrained device without post-issuance installation is presented. A manufacturer typically prepares the resource-constrained device by loading it with some initial content (310). This initial content typically includes the native OS, Java Card™ VM and some or all of the Java Card™ API packages (320). Some initial applets and/or libraries may be provided by an applet or library provider (315). The initial content is burned into ROM. This process of writing the permanent components into the non-mutable memory of a chip for carrying out incoming commands is called masking. The manufacturer may also load general data onto the card's non-volatile memory. This data is identical across a large number of cards and is not specific to an individual. An example of this general data is the name of a card manufacturer.
Typically, the manufacturer also personalizes the content of a card by assigning the card to a person. This may occur through physical personalization or through electronic personalization. Physical personalization refers to permanently marking by, for example, embossing or laser engraving the person's name and card number on the physical surface of a card. Electronic personalization refers to loading personal data into a card's non-volatile memory. Examples of personal data include a person's name, personal ID or PIN number, and personal key.
Next, an issuer 320 obtains an initialized device from the manufacturer. The issuer may obtain additional applets or libraries from a provider and load the additional content onto the device. This further customization of the cards is performed by installing the applets or libraries in the form of CAP files. The issuer may also load general data, such as the issuer name, into the card's non-volatile memory.
After preparing the cards (320), the issuer disables subsequent installation of libraries or applets on the device and distributes the device to an end user 325. At this point, the card is ready for use having its complete content. Since installation has been disabled, no further content will be added after the card has been issued. The card may be obtained from an issuer, or it can be bought from a retailer. Cards sold by a retailer can be general-purpose, in which case personalization is often omitted.
Turning now to FIG. 8, a block diagram that illustrates preparation of a resource-constrained device with post-issuance installation is presented. The diagram illustrates the case where a “trusted” installer 330 installs additional content on the device after the device has been issued to the end user 335. The post-issuance installer 330 is “trusted” because of a preexisting agreement between the post-issuance installer 330 and the issuer 340. In this case, the issuer 340 distributes the device to the end user 335 without disabling subsequent installations. The end user may update the content of the resource-constrained device by presenting it to a “trusted” post-issuance installer 330. The “trusted” post-issuance installer 330 installs additional content on the resource-constrained device and returns it to the end user 335. The installation is performed by transmitting a CAP file to the device.
In the scenario illustrated in FIGS. 7 and 8, the roles of the manufacturer, issuer, services provider and applet provider are described. These roles can be filled by one or more entities.
Typically, each of the roles described in FIGS. 7 and 8 entail testing the applets and packages before they are installed on the device. Testing checks the functional behavior of these modules, confirming that given a particular input a required output is produced. Testing examines a different domain than verification, described above.
A Java Card™ system may be constructed incrementally and at each stage, it is desirable to ensure program integrity. For example, the manufacturer may populate a resource-constrained device with one or more libraries. Before shipping, it would be desirable for the manufacturer to guarantee the content integrity. At this stage, there are only libraries on the device, and no applets. Without an applet, there is no applet entry point and therefore no execution path for a verifier to follow. If an issuer then adds an applet, it would be desirable continue to ensure the content integrity. Accordingly, a need exists in the prior art for a system and method for remote program verification that accounts for iterative installation. There is a further need for a system and method for resource-constrained device program verification that protects against untrusted post-issuance installers.
Binary Compatibility
In Java Card™ technology, a change to a type in a Java™ package results in a new CAP file. A new CAP file is binary compatible with a preexisting CAP file if another CAP file converted using the export file of the preexisting CAP file can link with the new CAP file without errors.
The Java™ Language Specification includes several examples of binary compatible changes for the Java™ language. These examples include adding a class and adding a field to a class. Examples of binary incompatible changes include deleting a class and changing the parameters to a method.
The Java Card™ Virtual Machine specification defines binary compatible changes to be a strict subset of those defined for the Java™ programming language. An example of a binary compatible change in the Java™ programming language that is not binary compatible in the Java Card™ platform is adding a public virtual method to a class that can be extended by a referencing binary file.
Turning now to FIG. 9, a block diagram that illustrates binary compatibility is presented. FIG. 9 shows an example of binary compatible CAP files, P1 (360) and P1′ (365). The preconditions for the example are: The package P1 is converted to create the P1 CAP file (360) and P1 export file (370), and package P1 is modified and converted to create the P1′ CAP file (365). Package P2 imports package P1, and therefore when the P2 CAP file (375) is created, the export file of P1 (370) is used. In the example, P2 is converted using the original P1 export file (370). Because P1′ is binary compatible with P1, P2 may be linked with either the P1 CAP file (360) or the P1′ CAP file (365).
The Java Card™ Virtual Machine further specifies that major and minor version numbers be assigned to each revision of a binary file. These version numbers are record in both CAP and export files. When the major version numbers of two revisions are not equal, the two revisions are not binary compatible. When the major version numbers of the two revisions are equal, the revision with the larger minor version number is binary (backward) compatible with the revision with the smaller minor version number.
The major and minor versions of a package are assigned by the package provider, A major version is changed when a new implementation of a package is not binary compatible with the previous implementation. The value of the new major version is greater than the version of the previous implementation. When a major version is changed, the associated minor version is assigned the value of 0.
When a new implementation of a package is binary compatible with the previous implementation, it is assigned a major version equal to the major version of the previous implementation. The minor version assigned to the new implementation is greater than the minor version of the previous implementation.
Both an export file and a CAP file contain the major and minor version numbers of the package described. When a CAP file is installed on a Java Card™ enabled device, a resident image of the package is created, and the major and minor version numbers are recorded as a part of that image. When an export file is used during preparation of a CAP file, the version numbers indicated in the export file are recorded in the CAP file.
During installation, references from the package of the CAP file being installed to an imported package can be resolved only when the version numbers indicated in the export file used during preparation of the CAP file are compatible with the version numbers of the resident image. They are compatible when the major version numbers are equal and the minor version of the export file is less than or equal to the minor version of the resident image.
Any modification that causes binary incompatibility in Java Card™ systems may cause an error at run time. Accordingly, an additional need exists in the prior art for a system and method for program verification that ensures binary compatibility.